The invention relates to an apparatus for converting a thermal scene into a visible image. The apparatus comprises an infrared objective, a pivotable mirror which can be pivoted back and forth about an axis, an infrared detection array which comprises a plurality of infrared detectors, and a linear display array which is connected to the infrared detection array via an amplifier arrangement. The radiation emitted by the linear display array is imaged in a plane of observation, preferably via the back of the pivotal mirror and via at least one diverting mirror.
Such apparatus is known as a "Common Module" and is described in, for example, an article entitled "Warmebildgerate aus--Common Modules--" by Manfred Hartl (Wehrtechnik, October 1980, pages 21 to 23). In such apparatus, which has a comparatively high resolution, the infrared detection array (to be cooled) is of a comparatively simple construction. The elements for forming the visible image are then physically combined with the infrared optical system and the infrared detection array.
Such apparatus is intended for viewing with a fixed direction of observation. However, it is frequently desired to provide the option of omnidirectional viewing. In conventional periscopes for visible light, in which the eyepiece and hence the plane of observation are fixed, this is achieved by rotating a mirror or a prism. In order to compensate for the image rotation an erecting prism is rotated along through half the angle. However, this principle cannot readily be applied to the present apparatus. This is because if the scanning direction of the pivotal mirror should not be rotated relative to the scene, the prism system which provides compensation for the image rotation would have to be arranged in the radiation path in front of the pivotal mirror. The prism system should then transmit infrared radiation and would therefore be very expensive. Moreover, this placement of the prism system gives rise to special problems because of vignetting, which in the case of viewing devices for visible light are less annoying and can be mitigated largely by simple means.